This invention relates to catheters useful for continuously monitoring the pressure of cerebro spinal fluid in a patient.
Various devices are currently available for monitoring intracranial cerebro spinal fluid (CSF) pressure in patients exhibiting symptoms of brain damage. The monitoring of CSF pressure is indicated where the surgeon suspects the presence of cerebral edema, an obstruction of normal CSF flow, blood clots, tumors, or other causes of increased pressure in the head of a patient. In many of these situations, it has been found that measurement of intracranial CSF pressure, as well as fluctuations in the pressure, can be exceedingly useful as a diagnostic tool, and that such measurements can yield valuable information when made either prior to or after craniotomy.
One type of pressure monitoring devices currently available comprises a fluid-filled, pressure indicating bladder which is placed within the skull, and is connected via a fluid couple to a pressure monitoring device. Examples of this type of device are disclosed in the Journal of Neurosurgery, Vol. 39 (Dec. 1973) at page 784, and in U.S. Pat. No. 3,877,137 to Hakim et al. Minaturized electronic transducers which may be implanted in the brain and electrically connected to the outside, as well as telemetric devices which require no direct connection to the exterior of the skull have also been proposed. These latter types of devices, having no fluid couple, are characterized by a potentially reduced infection risk, but also by the liklihood of electronic drift which results in instability and unreliability of the measurements they produce. Further, use of the telemetric type of device typically requires the head to be opened twice, once for insertion and once for withdrawal.
A serious problem in all of these devices is the possibility of infection. Whenever an incision is made through the scalp of a patient, there is a possibility that a staph or other infection may occur at the locus of the incision. Accordingly, when a short, direct tunnel through the scalp and skull is maintained over the period of monitoring, a path may be provided for the infection to migrate to the subdural space. Even more seriously, if the arachnoid membrane encasing the brain is penetrated, there is a possibility of infection within the brain itself.
Another type of monitoring device is described in the Journal of Neurosurgery, Vol. 39 (Sept. 1973) at page 416, wherein John K. Vries et al disclose a subarachnoid screw for monitoring intracranial pressures. This device comprises a hollow tubular metal structure designed to communicate between the subarachnoid space and the outside of the scalp. The proximal end of the screw consists of a standard luer lock and a hexogonal collar. The distal end has an open tip. Threads are provided adjacent the distal opening. To install the device, an incision is made in the scalp and a 1/4 inch hole is drilled through the skull. Prior to inserting the screw, the exposed dura is nicked with a knife and removed with a small angled curette. This maneuver usually also opens the arachnoid membrane, and a small amount of CSF is usually seen. The screw is then threaded into the hole so that its distal opening is in direct communication with the patient's CSF. In some cases, the arachnoid membrane is allowed to bridge the end of the hollow screw.
In use, the proximal end of the screw is connected to a stopcock assembly via a saline-filled extension tube. The stopcock connections include a pressure transducer, a 20 cc syringe filled with saline, and a water manometer which is open to the air through a bacteriologic filter. The output of the transducer is displayed on an oscilloscope and recorded on chart paper. The system is calibrated by zero balancing the transducer to the water manometer after matching up the height of the water manometer to the level of the end of the screw in the subarachnoid space. The transducer is then opened to the subarachnoid space via the saline-filled extension tube, and a calibrated intracranial pressure is recorded.
While the simplicity of this device makes it attractive, its use nevertheless still involves a significant infection risk since direct communication is established between the patient's subdural or subarachnoid space and the exterior of the scalp. On removal of the screw, the skin wound is sutured, but any infection which may occur at the wound during the monitoring procedures or thereafter has a short path to the interior of the skull.